1. Field of the Invention
The present invention relates to an aluminum substrate for an electrophotographic photoconductor, where a surface thereof is covered with an anodized aluminum film. Also, the present invention relates to an electrophotographic photoconductor using the aluminum substrate.
2. Description of the Related Art
Heretofore, technical advances in electrophotography have been made in the field of copier machines and recently have been applied in the field of laser printers and so on. The laser printers provide excellent image qualities and allow high speed and quiet printing operations in comparison with those of the conventional impact printers. Thus, most of the present recording devices, such as printers and copiers, adopt the electrophotographic technologies. A photoconductor to be provided in each of those recording devices is prepared by forming a photoconductive layer on a conductive substrate. Inorganic materials (e.g., selenium, zinc oxide, arsenic-selenium alloy, and cadmium sulfide) have been used for the conventional photoconductive layers. Recently, however, most of the photoconductive layers are prepared by using organic materials instead of inorganic materials because of:
(1) a wide choice of the organic materials; PA1 (2) an advantage in total expenditure including manufacturing costs; PA1 (3) the possibility of obtaining a novel photoconductor having excellent properties which are far superior to those of the inorganic one; and so on.
It is now common practice to make a photoconductor as a structure having functionally separated layers. That is, as shown in FIG. 2, the photoconductor comprises an under-coating layer 2, a charge-generation layer 3, and a charge-transport layer 4, which are stacked on a substrate 1 in that order. A single-layered type structure shown in FIG. 1 is used in some rare cases, where a layer 5 formed on a substrate 1 performs a double function.
For preparing the photoconductor having the functionally separated layers, materials to be applied on a surface of the substrate to form the under-coating layer as a first layer may be grouped into two types. The first one includes resin materials such as polyamide and melamine resins and the second one includes materials that make an anodized aluminum film on an aluminum substrate by means of anodic oxidation. In general, the latter type is more reliable under the conditions of high temperature and high humidity.
In the current trend of advanced information technology, the need for a multi-functional copier have been increased. The multi-functional copier may have a plurality of functions such as a facsimile function and a printer function in addition to a function of the conventional copier. Therefore, a digital copier is becoming a leading part as a multi-functional copier in the current trend of advanced information technology. The digital copier is designed to combine the conventional analog copier technology with the technologies of laser printer, LED printer, and so on, permitting the digitization of images.
Various materials can be considered in a photoconductor to be used in the laser printer or the LED printer. Among them, phthalocyanines are selected as materials of exceedingly sensitive to wavelengths generated by the laser and the LED, and thus they are often used in a charge-generation layer. Generally, the phthalocyanines are chemically stable, easy to synthesize, and obtainable at a comparatively low cost.
Using the known digital copier, where a photoconductor comprises phthalocyanine in its charge-generation layer, causes problems with a developed photographic image. A fog can be observed on the image after the first rotation of the photoconductor in the digital copier, while this kind of the trouble is almost trivial in the case of using the conventional laser or LED printer. Comparing with the results of the first rotation, furthermore, we can confirm that this kind of deficient image quality is reduced after the second rotation and substantially eliminated after the third rotation of the photoconductor.
The digital copier adopts a reverse development scheme which is generally used in the laser printers and the LED printers, so that it has been confirmed that the fogged image after the first rotation is substantially due to an electrostatic charge failure of the photoconductor.
Comparing with the results of the first rotation of the photoconductor before and after the process of continuously making about 100,000 copies of a predetermined material to experience electrical fatigue and letting it stand for about 30 to 60 minutes, the severity of the fog after the process becomes more worse than the severity of the fog before the process.
In laser printers and LED printers, we can observe the phenomenon of generating the potential difference between the charge potential at the first rotation and the charge potential at the second or later rotation. Thus, it is possible to redesign the process so that any rotations except the first one responsible for an image formation. In order to fill market needs for speeding up the first copy, accelerating the recovering time from a power-saving mode, and so on, there is the demand for designing the process so as to include the step of forming an image as a result of the first rotation. In this case, however, some modifications including a preliminary charging may be made. For attaining such a process design, however, the best possible solution is to reduce the difference between the potential at the first rotation and the potential at the second rotation in the photoconductor from the viewpoint of cost advantage and device simplification.